Boris Johnson and Michael Gove are 'leaning towards' supporting Britain's exit from the EU, it has emerged as David Cameron left for Brussels this morning for crunch talks with European leaders.

The pair are not impressed with the Prime Minister's efforts to make British law superior over EU law, according to friends.

If the pair decided to back Brexit, it would deal a major blow to the Prime Minister's hopes of keeping Britain in the EU.

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Boris Johnson (left) and Michael Gove (right) are 'leaning towards' backing Brexit, it emerged last night as Eurosceptics won over another influential voice in Penny Mordaunt (centre), the defence minister who starred in ITV diving show Splash two years ago

Mr Johnson's decision could be particularly decisive after a poll revealed that one in three people see him as 'important' to helping them decide which way to vote in the EU referendum, which is expected to be held in June.

News of another minister to back Brexit emerged this morning, with Penny Mordaunt, the Armed Forces minister who starred on the primetime ITV diving show Splash two years ago, being won over by Eurosceptics.

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David Cameron heads to Brussels to persuade his fellow 27 EU leaders to agree a deal

But talks hit a snag as it emerged other EU countries want a similar deal as Britain to limit benefits going to migrants, sparking opposition from Eastern Europe

EU Commission president Jean Claude Juncker said he was 'quite confident' a deal will be reached before the weekend

Influential Tory Tim Montgomery quit the party and dismissed the EU as 'the greatest source of social misery on the continent'

Former Labour leader Lord Kinnock warned of the 'seismic effects' of a Brexit

But former Chancellor Lord Lawson says leaving the EU would allow Britain to 'prosper and stand tall' in the world

David Cameron, pictured leaving Downing Street this morning, was told his plan to make British law superior over EU laws was unimpressive

Mr Johnson and Mr Gove want assurances from Mr Cameron that he end the practice of European courts overriding British law.

Judgments by the European Court of Human Rights that have caused outrage over recent years have included the decision to block the deportation of the radical preacher Abu Qatada and the attempt to force Britain to give prisoners the right to vote.

The move by European courts to block the deportation of Abu Qatada, pictured, caused outrage among Eurosceptics, who want to end the practice of UK courts being overruled by European judgements

The Court is not an EU institution and will not be reformed as part of Mr Cameron's talks in Brussels.

But in parallel to the agreement he hopes to secure, Mr Cameron has reportedly tasked Mr Gove with drawing up new laws in Britain which will be presented as part of a wider package of reforms.

A new piece of Commons legislation could be revealed by Mr Cameron as soon as tomorrow if he seals a deal in Brussels.

Earlier this month Mr Cameron promised to 'put beyond doubt' the sovereignty of the British Parliament after Mr Johnson demanded assurances.

But despite a 40-minute private meeting in Downing Street yesterday, it appears the Prime Minister has yet to convince the Mayor of London of his plans to reform Britain's membership of the EU.

And now he and Mr Gove are 'leaning towards the exit' due to the weakness of Mr Cameron's plans, two 'well-placed sources' told ITV News last night.

Mr Johnson has told reporters that he will make up his mind on which side of the referendum campaign to join when he finds out whether the sovereignty package is a 'bazooka or a popgun'.

At the weekend he made a further hint he would join the Out campaign after saying there was 'no reason to be afraid' of leaving the EU.

The London Mayor said he would 'come off the fence with deafening éclat' as soon as Mr Cameron secures a deal.

The uncertainty over two of the biggest Tory figures deals a blow to Mr Cameron's hopes of securing a deal that will persuade the British public to stay in the EU.

He will leave Downing Street around mid-morning and will hold a meeting with EU Council President Donald Tusk before EU leaders sit down to discuss the details of Britain's renegotiation.

Britain's membership is due to be top of the agenda at the summit and EU leaders hope to agree a deal by tomorrow morning, which would allow the Prime Minister to head home to kick-start the referendum campaign tomorrow.

He is expected to choose June 23 as the date of the referendum.

Nigel Farage, pictured, arrives in Brussels ahead of David Cameron's crunch summit with EU leaders. A poll yesterday found one in five people viewed him as 'important' in deciding which way they vote

But some diplomats in Brussels warned that there remained a 40 per cent chance of EU leaders failing to sign a deal this week, which would be disastrous for Downing Street and will risk having to push the referendum date into the autumn.

Details of the latest draft text of Mr Cameron's EU deal emerged overnight signalled another roadblock in the negotiations.

BORIS JOHNSON COULD SWING THE EU REFERENDUM RESULT, POLL FINDS

Boris Johnson, pictured leaving Downing Street yesterday, is seen as the second most influential politician in the EU referendum, according to a poll

The extend of Boris Johnson's influence on the outcome of the EU referendum was put in stark reality after a poll found one in three people see his decision as 'important' in helping to decide whether to vote In or Out.

An Ipsos MORI poll for the Evening Standard found that the Mayor of London is the second most influential politician on the EU vote - expected to be held in June.

David Cameron is the most influential figure, according to the poll, with 44 per cent of people saying he was significant in their decision.

Mr Johnson was important for 32 per cent, followed by Theresa May and George Osborne on 28 per cent, with Jeremy Corbyn on 27 per cent.

Their views on the referendum were deemed more important than the most significant Brexit campaigners, with just one in five people viewing Nigel Farage as playing an important role in helping them decide.

Former Chancellor Lord Lawson, who heads the Leave campaign, was chosen by 21 per cent of people, while the leader of the Britain Strong In campaign Stuart Rose was deemed important by just 23 per cent.

The poll also found that just one in three people have faith in the Prime Minsiter returning from Brussels tomorrow with a good deal.

Overall, the survey found that 51 per cent of people want to stay in the EU, opposed to 36 per cent who want to leave.

But many remain undecided and as the poll reveals, the role of individuals could have a significant impact on the result.

Plans to give Britain the ability to temporarily stop paying in-work benefits to EU migrants coming to the UK have been extended to all member states, which will be met with fierce opposition from eastern European countries.

INFLUENTIAL TORY QUITS PARTY OVER

Tim Montgomery, pictured, said he was leaving the party because of David Cameron's failure to build a socially just conservatism in office

An influential Tory quit the party today in protest at David Cameron's 'charade' EU reforms.

Tim Montgomery, the founder of the ConservativeHome website, Times columnist and former chief of staff to ex-Tory leader Iain Duncan Smith, announced he was leaving the 'Cameron project' in a column today.

He dismissed the EU as the 'greatest source of misery on the continent today' that had imposed 'intense austerity in countries such as Greece, and causing terrible youth unemployment across southern Europe from which millions will suffer lifelong scars.'

Mr Cameron's support for the EU was one of many of his social justice failures, Mr Montgomery wrote.

He hit out at the PM for having 'failed to build the socially just Conservatism that an extended period in power provided the space for'.

'Nothing registers more strongly on the social injustice front than recommending staying in the EU,' the Tory activist wrote.

And in a scathing final remark, Mr Montgomery added: 'I'm just glad that Mrs Thatcher cannot see what her party has become.'

Despite details of the deal yet to be finalised, politicians on both sides of the debate have stepped up their campaigning.

This morning the former Labour leader Neil Kinnock warned that Brexit would have a 'seismic' impact on the country.

'It [staying in or out of the union] matters a great deal particularly because focus of attention for 28 democracies is escalating and the effects therefore would be seismic for us in the UK – the choice of staying in or coming out,' he told the Today programme.

'It would be appalling for Britain [to leave the union] not least and I give you one figure…we sell 51 per cent of all export goods to the rest of European Union, they sell less than nine per cent all of export goods to us. In the event of us voting to be in or out of the union - 51 per cent is our need for them, nine per cent their need for us and you see who has the predominant hand in the negotiation.

'Our economic stability in particular is being put at risk and would be diminished because we would be excluding ourselves from the European Union and the world's biggest single market.'

'European Union is in constant state of change and form but doing it as an interested party [remaining in the UK] rather than a potential divorcee [would be best] but that's the hand that David Cameron has dealt for himself. I think he has done as well as possible in these conditions.'

But Lord Lawson, the former Tory Chancellor who is chairman of the Vote Leave campaign group, wrote an article in the Daily Telegraph today claiming Britain would 'prosper' and 'stand tall' in the world if it left the EU.

'Above all, we would become once again a self-governing democracy, with a genuinely global rather than a little European perspective,' he wrote.

'We would prosper, we would be free, and we would stand tall. That is what this referendum is all about.'

A previous version of this article made reference to judgements by the European Court of Justice rather than the European Court of Human Rights. We have updated the story accordingly.

MEANWHILE... BORIS JOHNSON'S DAD SAYS ENVIRONMENTAL CASE FOR STAYING IN MUST BE 'CLEARLY AND FORCEFULLY PUT'

Stanley Johnson, pictured with his son Boris, is a former MEP and today he made the environmental case for staying in the EU, warning Britain's clean beaches, air quality and animal welfare would be in jeopardy if it left

Boris Johnson's dad said today that the environmental case for staying in the European Union must be 'clearly and forcefully put' in the run-up to the referendum.

Stanley Johnson was announced as the chair of a new campaign group, Environmentalists for Europe (E4E) earlier this month and writing a piece today, he warned that Britain's air quality, beaches and animal would be put in jeopardy if it left the EU.

And he said it is 'fanciful' to believe that Britain's diplomatic power on environmental issues would be even half as effective outside the EU.

'E4E is determined that the environmental case for voting ‘In’...should be clearly and forcefully put in the run-up to the Referendum,' he wrote on PoliticsHome.

He added: 'By being 'in' we have improved our beaches, cleaned up the air we breathe, helped to preserve our wildlife and set standards for animal welfare.'

Mr Johnson served as a Tory MEP in Brussels from 1979-1984 and was previously head of pollution prevention in the European Commission.

His intervention today is another reminder of the risks Boris Johnson would be taking if he decided to join the Out campaign.

Not only would he risk division with his party leader, but also within his own family too.

WHAT DOES DAVID CAMERON STILL NEED TO SECURE FROM EU LEADERS TO DECLARE HIS DEAL IS DONE?

Mr Cameron's talks at the EU summit will involve both formal sessions and conversations in the margins with key figures - including Commission president Jean Claude Junker, centre, and Dutch PM Mark Rutte, right, pictured at a summit last year

David Cameron's deal with EU leaders is far from done and talks may go down to the wire tomorrow.

EU officials have scheduled a 'brunch' of English breakfast to nail down the final details.

Many points in the final document remain in 'square brackets', a mark in diplomatic circles indicated an unagreed point.

Government sources today insisted there was 'broad support' to find a way through on every point.

But there remains an impasse on several key areas:

Securing 'treaty change' on two points: the commitment to 'ever closer union' and how the eurozone works in relation to other national currencies like the pound.

The 'red card' mechanism for escalating issues of concern in member states to the European Council

The 'emergency brake' on restricting benefit payments to migrants. There are particular difficulties on how long this will last.

Exactly how child benefit will be 'indexed' to local rates and whether the change will apply to new migrants only or people already in Britain.

Government sources said: 'The PM will be battling hard on all of those areas, seeking to fix the issues that really matter to people here in Britain.'

The second draft of Mr Cameron's proposals highlighted problems around the deal on the currency, pictured. Government sources today made clear the issue was not yet resolved as the final summit began

THOUSANDS OF MILES AND COUNTLESS HOURS ON THE ROAD: HOW DAVID CAMERON GOT HIS DEAL ON EU MEMBERSHIP THIS FAR

Mr Cameron has met with German Chancellor Angela Merkel on many occasions during his renegotiation, most recently at last week's annual Matthiae-Mahlzeit dinner at the city hall in Hamburg, pictured

David Cameron has visited 20 European countries and met everyone of his 27 fellow leaders during his renegotiation tour.

As a deal inched closer to completion, Government sources spelled out the unprecedented diplomatic offensive embarked upon by Mr Cameron to get his agreement.

The final document is the first attempt to 'fundamentally reform' a country's membership of the EU from inside.

The source insisted no country had ever tried to renegotiate its membership before and pointed to successes secured on the single currency and sovereignty

The source said: 'The Prime Minister has really led the charge on this.

'He's taken a very personal involvement from the moment he was re-elected to meet and engage with European leaders.'

Mr Cameron has travelled far on wide during his talks, including to Hungary to meet Viktor Orban in January, left, and Portugal in September last year for talks with Pedro Passos Coelho

Earlier this month, Mr Cameron visited Poland for talks with Prime Minister Beata Szydlo on his deal as he worked to finalise the details ahead of today's summit

Mr Cameron has trekked to 20 different EU states for talks - many more than once.

The PM has met every EU leader twice during the talks, including 10 of them in Downing Street.

The renegotiation has been raised at 13 different world summits - either as the main business or in the fringes of unrelated gatherings.

And Mr Cameron has had talks on 'more than 26' occasions with the leaders of the European Commission, European Council and European Parliament.

The source added: 'He was the first Prime Minister to go to Austria in over 30 years. The first to go to Bulgaria and Romania in over 16 years. The first ever British Prime Minister to visit an independent Slovenia.'

David Cameron's EU deal hits ANOTHER snag as overnight changes will allow member states to limit benefits to migrants - sparking fury from eastern Europe

David Cameron, pictured leaving Downing Street this morning, faces another roadblock in his plans to reform Britain's membership of the EU

David Cameron's hopes of reforming Britain's membership of the EU hit another roadblock as he left Downing Street this morning for the most important Brussels summit of his premiership.

Draft changes to the deal released overnight have revealed that all member states would be allowed to restrict benefits to EU migrants.

These latest changes are likely to be fiercely opposed by eastern European countries, who fear millions of their citizens living in western European states will face discrimination over benefits.

In previous versions of the text the so-called 'emergency brake' would have only applied to Britain, Ireland and Sweden - the three member states that did not take advantage of transitional controls on EU migrants from Poland and nine other eastern European countries in 2004.

Countries such as Germany and Austria - overwhelmed by refugees fleeing the Middle East -demanded that they too can introduce temporary restrictions on EU migrants claiming in-work benefits.

The draft text, which was sent out to capitals in the middle of the night ahead of today's crunch summit in Brussels, also suggests that MEPs could have a veto over triggering the 'emergency brake'.

Previous plans only gave the European Parliament a say over the initial legislation, but the latest changes indicate they could block how countries such as the UK use the brake on migrants.

The latest changes are likely to make a deal more difficult to reach.

Romania voiced opposition to the latest changes this morning, worried that the ability of all member states to impose restrictions on benefits being paid to their citizens would harm the million Romanians currently living in Spain and Italy.

But speaking this morning, European Commission president Jean-Claude Juncker said he was 'convinced' that the UK would remain a 'constructive and active' member of the 28-nation bloc.

David Cameron is heading to Brussels for crucial talks with EU leaders, with key elements of his demands for change in Britain's relations with the EU still in dispute.

Mr Juncker said: 'I'm quite confident that we will have a deal during this European Council.'